The primary goal of our program is the understanding of how the auditory system extracts and encodes the invariant features of species-specific vocal signals and sound of biological significance. This research is based on our previous studies spanning the past several years. Our proposed work involves anatomical and electrophysiological recordings from single cells in the peripheral and central auditory system of crickets, fish, frogs and toads, reptiles and birds. This comparative approach is intended to provide insight into the evolution of auditory processing and the strategies of detecting communication signals of interest.